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Electronic Supplemental Information (ESI):
Improvement of the hole mobility of SnO epitaxial films grown by pulsed laser deposition
Makoto Minohara1*, Naoto Kikuchi1, Yoshiyuki Yoshida1, Hiroshi Kumigashira2,3, and
Yoshihiro Aiura1
1Electronics and Photonics Research Institute, National Institute of Advanced Industrial Science
and Technology (AIST), Tsukuba, Ibaraki 305-8568, Japan
2Photon Factory, Institute of Materials Structure Science (IMSS), High Energy Accelerator
Research Organization (KEK), Tsukuba, Ibaraki 305-0801, Japan 3Institute of Multidisciplinary Research for Advanced Materials (IMRAM), Tohoku University,
Sendai 980-8577, Japan
*Author to whom correspondence should be addressed; [email protected]
This PDF file includes:
Figures S1, S2, S3, S4 and S5
Reference S1
Electronic Supplementary Material (ESI) for Journal of Materials Chemistry C.This journal is © The Royal Society of Chemistry 2019
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Survey of the optimum growth conditions for SnO film grown on LaAlO3 (001) substrate
Figure S1 shows the growth condition dependence in XRD patterns of the grown films.
At Tg = 500 ºC, which is close to the conventional growth temperature of 575 ºC, lots of peaks can
be observed, indicating there is no optimum condition for the growth of SnO single phase. The
intensity of (00l) Bragg peaks of SnO become stronger by decreasing Tg together with PO2, however,
other SnO Bragg peaks and other phases are still observed. Eventually, the SnO single phase can
be obtained at Tg = 350 ºC with PO2 in the range between 2´10−2 to 8´10−2 Pa, while the b-Sn
exists at PO2 = 1´10−2 Pa. Among them, the SnO film grown at PO2 = 4´10−2 Pa showed
sufficiently low resistance at room temperature for reliable measurements using electric
transport option with four-probe method attached on to the Physical Property Measurement
System (Quantum Design, Dynacool). Therefore, we chose Tg = 350 ºC and PO2 = 4´10−2 Pa
as the optimum condition for single phase SnO epitaxial film.
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Figure S1. XRD patterns of the grown films on a LaAlO3 (001) substrate at various Tg and
PO2. The asterisks indicate the peaks originated by Cu Kb radiation.
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Angular dependence of PES spectra for a Sn-3d core level
Figure S2 shows angular dependent PES spectra from the SnO film for a Sn-3d5/2
core level. Since the intensity of the peaks at higher (lower) binding energies becomes
stronger (weaker) with increasing photoelectron emission angle q, the higher (lower) peaks are
assigned to the surface (bulk) components.
Figure S2. Angular (surface-sensitivity) dependent PES spectra from the SnO film for a
Sn-3d5/2 core level. The empirical spectrum can be fitted using two curves shaded with
gray and red.
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Analysis of the angular dependence of PES spectra for a Sn-3d core level
In general, the total core-level photoemission signal I can be written as the
summation of a core-level spectrum emitted from each atomic layer:
𝐼 = ∑ exp(−𝑛𝑙/𝜆 cos 𝜃)3456 , (1)
where n is number of the n-th layer from the surface and l is the distance between the
neighboring atomic layers, the height of a single unit cell of assumed crystal structure. l is the
characteristic probing depth based on the theoretical study of Tanuma et al.,S1 and q is the
photoelectron emission angle with respect to the surface normal. In order to evaluate the
thickness of the surface layer, the equation (1) is extended as
𝐼7 𝐼8⁄ = :𝑎 <∑ exp = >4?@A@ BCDE
FG456 HI / :(1 − 𝑎) <∑ exp = >4?K
AK BCDEF3
45GLM HI, (2)
Subscript S and B means to surface and bulk layer, respectively. a and d correspond to the
coverage and the thickness of the surface layer, respectively. By changing a and d as a free
parameter for the simulation, we estimated at most 2-unit cells for the surface Sn4+ region.
The schematics for the characterization setup for the electrical measurement
Figure S3. Schematic picture for the Hall measurements.
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XRD patterns of SnO film grown on YSZ (001) substrate for various growth temperature
Figure S4a shows 2q-q XRD pattern of SnO film grown on YSZ (001) substrate.
The lattice constant, which is estimated from (00l) Bragg peaks, as a function of the growth
temperature is shown in Fig. S4b. The lattice constant is close to the bulk value at Tg = 350 ºC.
Above (below) this temperature, the lattice constant becomes smaller (bigger). This strongly
suggests that the amount of defect (such as Sn or O vacancy) changes by changing the growth
temperature.
Figure S4. (a) XRD patterns of the grown films on a YSZ (001) substrate at various
growth temperature Tg. The asterisks indicate the peaks originated by Cu Kb radiation. (b)
Estimated lattice constant from (00l) Bragg peaks in Fig. S4a. Broken line corresponds to the
reported lattice constant of bulk SnO.
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The effect of growth temperature on the carrier density of SnO films
Figure S5 shows the carrier density of single-phase SnO films which are grown on
YSZ substrate as a function of the growth temperature (see also Fig. S4). The carrier density
clearly decreases with decreasing the growth temperature. Therefore, we are convincing that
the growth temperature plays an important role to suppress the carrier density. Considering the
hole carrier density increases with increasing the growth temperature and the facts that the
SnO2 appears at a higher growth temperature range (Tg ≥ 450 ºC), we can deduce that Sn
concentration becomes relatively poor (rich) with increasing (decreasing) the growth
temperature.
Figure S5. Carrier density of single-phase SnO films grown on YSZ substrate as a
function of growth temperature.
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References
R1 S. Tanuma, C. J. Powell, and D. R. Penn, Surf. Interface Anal., 2003, 35, 268.